Bi-directional amplifying systems



Jan. 5, 1965 P. J. READ 3,164,679

BIE-DIRECTIONAL AMPLIFYING SYSTEMS Original Filed May l5, 1961 2 Sheets-Sheet 1 ATTORNEY Jan. 5, 1965 P. J. READ 3,164,679

BI-DIRECTIONAL AMPLIFYING SYSTEMS Original Filed May 15, 1961 2 Sheets-Sheet 2 PING' Q n N il l t n *w inventor:

P. J. Read. Z//x 241m.

ATTORNEY United States Patent O lee med ,ff

3,164,679 BI-DIRECTIONAL AMPLIFYIN G SYSTEMS Phillip J. Read, Ottawa, Ontario, Canada, assignor to Northern Electric Company, Limited, Montreal, Que hec, Canada, la corporation of Canada Continuation of application Ser. No. 109,905, May 15, 1961. This application lune 15, 1964, Ser. No.

1s Creams.` (ci. 179-16)V This invention relates to telephone systems and more particularly to transistor` bi-directional amplifying circuits employed therewith. This application Vis a continuation of my original application, Serial No. 109,905, filed May 15, 1961, now abandoned. j In long-line telephone circuits, it isnecessary to arnplify the ringing signals transmitted from the central office and to reshape the dialling pulses generated by a subscriber. In such circuits, it has been the general practice to carry out these functions at a point between the central oflice and the subscribers station. This arrangement heretofore involved the use of mechanical elements which, due to their large size and the necessity of mechanical adjustment, have generally not been too successful.

An object of this invention is to provide a telephone system which includes a bi-directional amplifier transistor circuit adapted to transmit dialling pulses from the subscribers station to the central oiiice and ringing signals in the opposite direction.

Another object of the invention is to provide a telephone system having the foregoing properties adapted to allow increase of the loop resistance whilst maintaining the same loop current.

These and other objects of this invention are attained by providing within an automatic telephone system which includes the combination of a dial pulse input circuit and a ringing current output circuit, and the combination of a ringing current input circuit and a dial pulse output circuit, amplifying means comprising a rst amplifier means, controlled by the subscribers loop circuit, and a second amplifier means, controlled by the ringing energy from the central office, and a ldiode bridge clonnected into the circuit so as to steer, in one direction through the circuit, the supervising current from the central ofce.

A better understanding may be had by referring to the following description, taken in conjunction with the drawings in which like references refer to like parts, in which:

FIG. 1 illustrates a telephone system in block form showing only the essential elements to define the invention and including an intermediate station, in which the invention is represented; and

FIG. 2 illustrates a schematic circuit of the intermediate station.

Considering the drawings, there is shown a central office 1, having a reversible potential source 2, which may be 48 volts, a ringing source 3, which may be up to of the order of 100 `volts R.M.S., selector switches 4, terminals 5, 6. Also shown is subscribers station 7, having switchhook 8, receiver 9, impulse dial lil, resistor 11, capacitor 12, ringer 13, terminals 14, 15. interposed between the central office 1 and substation 7 is an intermediate station 16 having terminals 17, 18 and 19, 20.

In this example, central oflice 1 has selector switches 4 which may be operated by dial pulses, and a source of ringing current 3 Awhich may be transmitted to subscribers unit 7, Therefore, conductors terminating at terminals 5 and 19, and 6 and Ztl respectively, comprise the first and second dial pulse input circuit and ringing current output circuit conductors. Conductors terminating at terminals 7 and 14, and 18 and 15 respectively, comprise the rst and second ringing input current circuit and dial pulse output circuit conductors.

In FIG. 2 there is shown a complementary pair of transistors consisting of first and second transistors 22, and 21 and a third transistor 23 each having emitter, collector and base electrodes 27, 28, 29 and 24, 25, 26 and 36, 31, 32 respectively.

Also shown is transformer windings 42 and 43 and a bridge circuit, connected thereto consisting of a first and second semi-conductor diode 33, 34 having Vtheir cathodes connected together to form a first junction point 35, a third and fourth semi-conductor diode 36, 37 individually connected in series and in the same polarity with -the first and second diode 33, 34 to form a second and third junction point 38, 39. The free ends of the diodes 36, 37 are connected together to form a fourth junction point 40.

The iirst and fourth junction points 35, 4G are connected to the emitter 24 through optional resistor 41, and to collector 25 of transistor 21 respectively, while the second and third junction points 38, 39 are connected to the tip and ring side ofthe central otiice conductors, first and second conductors of the dial pulse output circuit, through the transformer winding 42 and through optional resistor 43 and other transformer winding 42. Resistors 41 and 43 may be inserted in the circuit to increase the dial pulseoutput circuit resistance.

Also shown are iirst and second direct current sources 44, 45 connected with opposite poles to ground. The emitter 27, collector 28 and base electrodes 29 of transistor 22 are connectedto the first energy source 44, to the base electrode 26, of transistor 21 through protection resistor 46, and to one conductor of the subscribers loop, the dial pulse input circuit, throughresistor 47 and coupling winding 48 respectively. The other conductor of the subscribers loop is connected to the second energy source 45, through resistor 49 annd transformer Coupling winding 48.

Considering the third transistor 23, the emitter 3G, collector 31 and base electrode 32. are connected to the first energy source 44, resistor 49 and the third junction point 39 respectively. A limiting diode 50 is connected between the emitter 30 and base 32 ofV transistor- 23. Resistor 51 is connected between the emitter and base electrode 30 and 29 of transistors 23 and 22 respectively.

Also shown is a potential dividing circuit consisting of the coupling capacitorV 52 connected between the base electrode of transistor 23 and junction point 39, resistor 43 and capacitor 53 connected between the junction point 39 and the coupling coil winding 48. Capacitors 54,' 55 are audio by-passing capacitors.

A transformer having primary winding 42 and secondary Winding 48 may be used to transfer signals other than dial pulses or ringing current (voice signals, for instance) across my amplifying means. One embodiment of this provides a transformer having a split primary winding and split secondary winding. Each coil of the primary winding 42 is connected in series with a conductor of the ringing current input circuit, and each coil of the secondary winding 48 is connected in series with a conductor of the dial pulse input circuit. By-

pass capacitors 54 and 55 are connected between each conductor o-f the ringing input circuit and eachV conductor of the dial pulse input circuit respectively. Thus,

-it may beseen that voice signals can be transferred from On Hook In the idle condition, the potential at the base electrode 29 of transistor 22 is held close to the potential of the l' Y 3 n energy ysource 44 by the action of lresistor Si. Consequently the emitter-base junction 27-29 in transistor 22 is reversely biased so that no current will flow through the collector-emitter 28-27 of transistor 22. As no current flowsfrom the base 26 of transistor 21, no current can flow from the emitter 24 to the collector 25 of transistor 21. FDhus only leakage current may pass from the energy source 2 in the central otlce 1, through the diodes 33, 37, the diodes 34, 36 being reversed biased and therefore non-conducting.

O H ook When the subscriber at substation 7 lifts his switchhook, the loop circuit 45-49-48-171411-8-9-15-18- V48-47-51444 is closed. The current flowing in this circuit causes the potential at the base 29 of transistor 22 to rise so that the base-emitter junction 29-27 is forward biased allowing current to flow through resistor 46 and the collector 28, and emitter 27 of transistor 22. Thus, current is allowed to iiow through the emitter 24 tothe collector 25 of*y transistor 21. Since one or the other conductor of the dial pulse input circuitis effectively connected to ground at the central office, current can flow from ground through the diode bridge circuit, through emitter 24, base 26, resistor 45, collector 28 of transistor 22, emitter 27 and through current source 44 to ground. An energized circuit is now completed over the path 4 5-19-42-38 33-35 41-24-25-40-37-39-43-42- -6-4-3-2 The current through this circuit operates the selector switches 4. As the subscriber operates his dial 10, the above loop opens and closes, setting the Yselector switches 4 at the central oiice 1. When the called party at the central oflice 1 responds to the call, the polarity at energy source 2 is reversed so that diodes 34, 36 conduct and diodes 33, 37 do not conduct.

Ringing I In signalling the subscriber at the subscribers station 7, the signalling energy is transmitted over the line ringing current inputl circuit, from generator 3 through 5, 19, 6 and 20 t0 the intermediate office 16. Part of the signalling energy is applied to the capacitor 52 and to the base 32 of transistor 23 where the voltage excursion is limited by the action of diode 50. Of course, diode 50 can be left out and transistor 23 be driven to saturation and olf for limiting action. Another part of the Aringing energy is coupled to the subscribers ring lead by capacitor 53. Y Y

In order that the potential generated by the generator 3 does not exceed the reachthrough potential of transistor 23, the Iresistance of resistor 43 and the parallel impedance of capacitors 52 and 53 are arranged to form a potential divider which reduces the alternating potential at the cathode of diode 5t) by the required amount.

VResistor 46 protects transistors 21 and 22 against collectoremitter reachthrough potentials.

Due to the high current gain (about 50) of transistor 253, ringing current which drives the transistor off and into saturation results in a limited signal developed across the load resistor 49. The voltage applied to the ringing current output circuit at terminal 17 is caused to swing between that supplied by source 44 and source 45. This resulting alternating current is transmitted along the subscribers tip lead 17-14 and causes the bell in the ringer A13 to sound. The values of resistors 49V, 47 and 51 are 4 Y I effectively degrees out of phase with that fed back from the ringing current output circuit. This phase reversal occurs because transistor 23 causes a 18() degree phase change during amplification of the ringing current. Thus, the two ringing current components effectively cancel each other such that transistors 21 and'22 do not conduct effectively from ringing current alone. However, if direct current is allowed to flow in the dial pulse input circuit due to, say, a subscriber answering his telephone, closing the subscribers loop, the direct potential appearing across voltage divider resistors 47 and 51 will cause transistors 21 and 28 to conduct, allowing current to flow through transistor 21 from the dial pulse output circuit. This current may, for instance, be used to operateV external means to shut off the ringing current generator 3.

What is claimed is:

l. In an automatic switching telephone system, which includes a central oil'ice which includes a direct current source of reversible polarity, a ringing current source, selection switches, a subscribers station, and a transmission line comprising a tip andv ring lead, an intermediate circuit for relaying supervisory signals over the transmission line comprising:

a first and second transistor which are a complementary a solid bridge rectifying bridge circuit consisting of a first and second semiconductor diode, an electrode of one being connected to a like electrode of the other to form a first junction point, a third and fourth semi-conductor diode connected in serieswith and in the same sense with the first and second diode respectively to form a second and third junction point respectively, the remaining unconnected elec trodes being connected together to form a fourth junction point,

a means for connecting the first and fourth junction point to the emitter and collector electrodes of the rst transistor respectively,

a first coupling means for connecting the second and third junction points to the tip and ring leads extending to the central office, respectively, means included in the coupling means to by-pass audio frequencies,

a first and second energy source opposite in polarity,

a means for connecting the collector and emitter electrodes of the second transistor to the base ,electrode of the first transistor and to the first source respectively, Y

a second coupling means for connecting the subscribers station ring lead to the base electrode, through a first load resistor, of the second transistor, the junction point of such electrode and resistor forming a fifth junction point which is connected to the first energy source and to the third junction point and for connecting the tip lead, through a second resistor, to the second energy source, means included in the second coupling means to by-pass audio frequency.

2. An automatic switching telephone system in accordance With claim l comprising in combination: a third transistor of like conductivity to the second transistor, in which the emitter is connected to the first source and the collector through the said second .load resistor to the second source; a third coupling means for connecting the base of the third transistor to the third junction point; a fifth resistor connected to the base-emitter electrodes of the third transistor.

3. An automatic switching telephone system in accordance with claim l having means to amplify the ringing signals comprising in combination: a third transistor of like conductivity to the second transistor, in which the emitter is connected to the rst source and the collector through the said second load resistor to the second source; a third coupling means for connecting the base of the third transistor to the third junction point; a fifth diode of like material to the third transistor connected in parallel relation and oppositely poled to the base-emitter electrodes of the third transistor.

4. An automatic switching telephone system ,in accordance with claim 3, in which the said ringing signals include a direct current component: a means for initiating ringing tripping which comprises a third resistor connected between the fifth junction point and the first energy coupling means.

'5. In a circuit in accordance with claim 4: means to prevent the reachthrough potentials of the saidfirst and second transistors from being exceeded, comprising in combination a potential divider consisting ofl a fourth resistor included in the said first coupling means for connecting the said third junction point to the central omce and the parallel combination of said third coupling means, which includes a capacitor connected between the base electrode of the second transistor and the third junction point, together with the said coupling capacitor connected between the said third junction point and the subscribers station ring lead.

6. In an automaticvswitching telephone system which includes the combination of a dial pulse input circuit and a ringing current output circuit, and the combination of a ringing current input circuit and a dial pulse output circuit, amplifying means for dial pulses and ringing current comprising:

(a) a source of direct current connected to the dial pulse input circuit, (b) first amplifier means having an input circuit and an output circuit, operative to amplify dialing pulses,

and to allow current to fiow and stop current from flowing in the dial pulse output circuit when current is flowing and not iiowing respectively in the dial puise input circuit, andl (c) second amplifier means having an input circuit and an outputcircuit operative when ringing current is conducted throughV the ringing current input circuit to cooperate with said source of directV current and apply amplified ringing current to theringing current output circuit.

7. Amplifying means as defined in claim 6 comprising means to effectively cancel ringing current which may be amplified by the first amplifier means.

8. Amplifying means as defined in claim 7 wherein a proportion of ringing current effectively 180 degrees out of phase with the ringing current to be Iamplified by said second amplifier means, is `fed to the input circuit of said first amplifier means so as to cancel enough ringing current which may be flowing therein to prevent the first amplifier means from allowing significant direct current flow in the dial pulse output circuit.

9. Amplifying means for dialing pulses and ringing cur-rent as defined in claim 6, comprising means to cause unidirectional current to flow in the output circuit of the first ampiifier means when current flowing in the dial pulse output circuit flows in a forward or reverse direction.

V1t). Amplifying means :as defined in claim 9 wherein said means to cause unidirectional current to ow in the output circuit of the first amplifier means is a diode bridge circuit interposed between the output circuit of the first amplifier means and the dial pulseoutput circuit.

11. In a combination with amplifying means as defined in claim 6, bypass means to allow signals other than dial pulses and ringing current to bypass the amplifying means. Y

l2. The combination including amplifying means as defined in claim y11 wherein said bypass means comprises a transformer having a primary and secondary winding, and two capacitors; the primary winding being connected in series with one capacitor across the dial pulse input f5 circuit, and the secondary winding being connected in series with the second capacitor across the ringing cur- -rent input circuit.

13. In an automatic switching telephone system which includes the combination of a dial pulse input circuit and ringing current output circuit having a first and second conductor, and a ringing current input circuit and a dial pulseoutput circuit having a third and fourth conductor, first amplifying means `for dial pulses comprising:

(a) a first amplifier means compris-ing first and second transistors which are a complementary pair, having means connectingthe collector of the 'first transistor to the base of the second transistor,

(b) a bridge rectifier having input and output conductors, connected with its input conductors to the conductors of the dial pulse output circuit, and its output conductors to the collector and emitter respectively of the second transistor to form a first amplifier means output circuit, a first current source connected between ground and the emitter of the first transistor, a first `and second resistor in series connected between the first conductor of the dial pulse input circuit and the emitter of the first transistor, ythe junction point of the two resistors being connected to the lbase of the first transistor;

(c) a second direct current source connected in series with a third resistor bet-Ween the second conductor of the dial .pulse input circuit and ground; the second current source being poled in such direction that it will be series` aiding with the first direct current source as viewed from the -iirst and second conductor `of the dial pulse input circuit.

14. In an amplifying means as defined in claim 13, Where the means connecting the collector of the rst transistor to the base of the second transistor is a third resistor adapted to cause reduction of potential appearing between electrodes of the first and second transistors to a value less than that encountered at breakdown thereof.

l5. In an automatic switching telephone system comprising fir-st amplifying means as defined in claim 1-3, second amplifier means for ringing current comprising a third transistor of like polarity to the first transistor, 4with its collector connected to the junction of the third resistor and the second conductor of the ringing current output circuit, its emitter electrode connected to the emitter electrode of the first transistor, a first capacitor connected between one conductor of the ringing current input circuit and the base electrode of the third transistor, and a fourth resistor connected between the ibase and emitter electrodes `of the third transistor.

'16. Amplifying means as defined in claim 15 wherein a diode is connected in parallel with the fourth resistor, poled oppositely to the diode yformed by the lbase-emitter junction ofthe third transistor.

17. Amplifying means as defined in claim 15 wherein a second capacitor is connected between the junction of the first capacitor and one conductor of the ringing current input signal, and the conductor of the ringing current output circuit which lis'connected to the 'first resistor.

18. Amplifying means as defined in claim 17 comprising a transformer having a split primary winding and a split secondary Winding, each coil of the secondary Winding Ibeing connected in series with one conductor of the dial pulse input circuit respectively and each coil of the primary winding lbeing` connected in series `with one conductor of the ringing current input circuit respectively, and a third and fourth capacitor, the third capacitor being connected across the dial pulse input circuit and the fourth capacitor being connected across the dial pulse output circuit.

No references cited.

ROBE-RT H. ROSE, Primary Examiner. 

1. IN AN AUTOMATIC SWITCHING TELEPHONE SYSTEM, WHICH INCLUDES A CENTRAL OFFICE WHICH INCLUDES A DIRECT CURRENT SOURCE OF REVERSIBLE POLARITY, A RINGING CURRENT SOURCE, SELECTION SWITCHES, A SUBSCRIBER''S STATION, AND A TRANSMISSION LINE COMPRISING A TIP AND RING LEAD, AN INTERMEDIATE CIRCUIT FOR RELAYING SUPERVISORY SIGNALS OVER THE TRANSMISSION LINE COMPRISING: A FIRST AND SECOND TRANSISTOR WHICH ARE A COMPLEMENTARY PAIR, A SOLID BRIDGE RECTIFYING BRIDGE CIRCUIT CONSISTING OF A FIRST AND SECOND SEMI-CONDUCTOR DIODE, AN ELECTRODE OF ONE BEING CONNECTED TO A LIKE ELECTRODE OF THE OTHER TO FORM A FIRST JUNCTION POINT, A THIRD AND FOURTH SEMI-CONDUCTOR DIODE CONNECTED IN SERIES WITH AND IN THE SAME SENSE WITH THE FIRST AND SECOND DIODE RESPECTIVELY TO FORM A SECOND AND THIRD JUNCTION POINT RESPECTIVELY, THE REMAINING UNCONNECTED ELECTRODES BEING CONNECTED TOGETHER TO FORM A FOURTH JUNCTION POINT, A MEANS FOR CONNECTING THE FIRST AND FOURTH JUNCTION POINT TO THE EMITTER AND COLLECTOR ELECTRODES OF THE FIRST TRANSISTOR RESPECTIVELY, A FIRST COUPLING MEANS FOR CONNECTING THE SECOND AND THIRD JUNCTION POINTS TO THE TIP AND RING LEADS EXTENDING TO THE CENTRAL OFFICE, RESPECTIVELY, MEANS INCLUDED IN THE COUPLING MEANS TO BY-PASS AUDIO FREQUENCIES, A FIRST AND SECOND ENERGY SOURCE OPPOSITE IN POLARITY, A MEANS FOR CONNECTING THE COLLECTOR AND EMITTER ELECTRODES OF THE SECOND TRANSISTOR TO THE BASE ELECTRODE OF THE FIRST TRANSISTOR AND TO THE FIRST SOURCE RESPECTIVELY, A SECOND COUPLING MEANS FOR CONNECTING THE SUBSCRIBER''S STATION RING LEAD TO THE BASE ELECTRODE, THROUGH A FIRST LOAD RESISTOR, OF THE SECOND TRANSISTOR, THE JUNCTION POINT OF SUCH ELECTRODE AND RESISTOR FORMING A FIFTH JUNCTION POINT WHICH IS CONNECTED TO THE FIRST ENERGY SOURCE, AND TO THE THIRD JUNCTION POINT AND FOR CONNECTING THE TIP LEAD, THROUGH A SECOND RESISTOR, TO THE SECOND ENERGY SOURCE, MEANS INCLUDED IN THE SECOND COUPLING MEANS TO BY-PASS AUDIO FREQUENCY. 